To put another spin on this thread:
Sonny's gaffe, and the greed it betrayed, was the cornerstone of Sol's decision to kill Vito. Sol was convinced that Sonny could be persuaded to settle with him, rather than to go to war. No doubt that's exactly what he told Tatt and perhaps the other Dons: there will be no war because Sonny is hot for my deal.
Suppose Sonny had kept his mouth shut. Do you think Sol still would have attempted to kill Vito? Would the others have gone along with it?
If Sonny had kept his mouth shut, I'm of the mind that Sollozzo would've had to refrain from whacking Vito. The other families wouldn't have sanctioned the hit if they thought it would only lead to all out war. Sollozzo would have nothing to gain from it, since doing so would not net him the contacts and financing he wanted.
